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NERSC Helps Expose Cosmic Transients

Finding fleeting cosmic events not only requires the right kind of telescope and camera, it depends on high-performance computing to pinpoint objects of interest among thousands of images while there’s still time for follow-up observations. Caltech and NERSC join forces in just such a search, the Palomar Transient Factory.

This false-color image of our glowing galactic neighbor, the Andromeda Galaxy, was created by layering 400 individual images captured by the PTF camera in February 2009. In one pointing, the PTF camera has a seven-square-degree field of view, equivalent to approximately 25 full moons. (Palomar Transient Factory/Peter Nugent, Berkeley Lab)

BERKELEY, CA – An innovative new sky survey, called the Palomar Transient Factory (PTF), will utilize the unique tools and services offered by the U.S. Department of Energy’s (DOE’s) National Energy Research Scientific Computing Center (NERSC) at Lawrence Berkeley National Laboratory (Berkeley Lab) to expose relatively rare and fleeting cosmic events, like supernovae and gamma ray bursts.

In fact, during the commissioning phase alone, the survey has already uncovered more than 40 supernovae, stellar explosions, and astronomers expect to discover thousands more each year. Such events occur about once a century in our own Milky Way galaxy and are visible for only a few months.

“This survey is a trail blazer in many ways – it is the first project dedicated solely to finding transient events, and as part of this mission we’ve worked with NERSC to develop an automated system that will sift through terabytes of astronomical data every night to find interesting events, and have secured time on some of the world’s most powerful ground-based telescopes to conduct immediate follow up observations as events are identified,” says Shrinivas Kulkarni, a professor of astronomy and planetary science at the California Institute of Technology (Caltech), and Director of Caltech Optical Observatories. He is also principal investigator of the PTF survey.

“This truly novel survey combines the power of a wide-field telescope, a high-resolution camera, and high-performance network and computing, as well as the ability to conduct rapid follow-up observations with telescopes around the globe for the first time,” says Peter Nugent, a computational staff scientist in Berkeley Lab’s Computational Research Division (CRD) and the NERSC Analytics Group. Nugent is also the Real-time Transient Detection Lead for the PTF project.

Every night the PTF camera – a 100-megapixel machine mounted on the 48-inch Samuel Oschin Telescope at Palomar Observatory in Southern California – will automatically snap pictures of the sky, then send those images to NERSC for archiving via a high-speed network provided by DOE’s Energy Sciences Network (ESnet) and the National Science Foundation’s (NSF’s) High Performance Wireless Research and Education Network (HPWREN).

At NERSC, computers running machine-learning algorithms in the Real-time Transient Detection pipeline scour the PTF observations for “transient” sources, cosmic objects that change in brightness or position, by comparing the new observations with all of the data collected from previous nights. Once an interesting event is discovered, machines at NERSC will immediately, within minutes, send its coordinates to Palomar’s 60-inch telescope and others for follow up observations.

“PTF is an example of the growing need to provide data services for science; it combines automated, real-time analysis with high-end systems and networks in a way that changes the way the scientific community works,” says NERSC Director Kathy Yelick.

“We are currently uncovering one event every 12 minutes. This project will be keeping the astronomical community busy for quite a while,” says Kulkarni.

“These tools are extremely valuable because they not only help us identify supernova, they uncover them while the star is in the act of exploding,” says Robert Quimby of Caltech, who is the software lead for the PTF program. “This gives us valuable information about how cosmic dust is spread across the universe.”

He notes that all chemical elements in the universe besides hydrogen and helium are created inside stars. When massive stars die in fiery supernova explosions, they blast these chemical creations out into space. The cosmic dust will eventually come together to form stars, planets, comets – even humans. Everything around us is made of stardust.

In addition to spreading stardust across the cosmos, some species of supernovae also play a vital role in helping us understand the nature of the universe. For example, because Type Ia supernova are relatively uniform in brightness, they act as cosmic lighthouses, helping astronomers judge distance. Many astronomers participating in the PTF survey are specifically searching for these cosmic creatures.

“It is very exciting to find so many supernovae, so early in the project. It’s like we’ve just turned on the spigot and are now waiting for the fire hose to blast,” says Quimby.

Astronomers using NERSC’s Real-Time Detection pipeline uncovered supernova SN2009av-1a in the act of exploding. At left, the image of a galaxy 800 million light-years away was created by layering observations taken by the Palomar Transient Factory camera from February 23-27. Second from left is the image captured by the PTF camera on February 28. Next, using the NERSC pipeline to digitally subtract the earlier image from the new one, scientists exposed this cosmic transient, a supernova. At right, subtracting the previous images from one taken March 2 showed the source getting brighter. Follow-up observations caught the Type Ia supernova, now called SN2009av, at peak brightness. (Palomar Transient Factory/Dovi Poznanski, Berkeley Lab)

PTF is a collaboration of Berkeley Lab, Caltech, Columbia University, the NSF’s HPWREN, the Infrared Processing and Analysis Center, Las Cumbres Observatory Global Telescope Network, Oxford University, University of California at Berkeley, and the Weizmann Institute of Science, Israel. PTF is partly supported by DOE’s Scientific Discovery through Advanced Computing program; NERSC provided the storage and systems infrastructure. NERSC and ESnet are managed by the Berkeley Lab on behalf of the Office of Advanced Scientific Computing Research within the DOE Office of Science.

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